The present invention relates to a feature data management method in graphic processing systems such as a Geographic Information System (GIS) and Computer Aided Design (CAD), and particularly to a method for efficiently managing data changing with time, such as changes of a view of a town caused by the construction and removal of houses.
In a department of local autonomies and the like that use geographic information, it is important to store past history information. Facility management requires to keep track of maintenance information and utilization status of the past, while in city planning, the history of city changes is useful for the analysis of current situation and the prediction of the future.
Heretofore, local autonomies and the like have managed the geographic information with paper maps in such a manner that (1) change portions are written directly to maps, (2) the maps are wholly rewritten once every several years, and (3) past paper maps are stored in a warehouse. However, this method requires considerable efforts to search past maps and provides a heavy load to store a large number of past maps.
Recently, a Geographic Information System (GIS) built upon an electronic version of paper map has been developed and used. The GIS handles an electronic version of paper map, resulting in easier update of maps and the storage and search of past maps in comparison with paper maps.
Conventional GISs, to store past geographic information, have employed a method of backing up the contents of geographic information database (DB) to external storage media such as digital audio tape (DAT) regularly, for example, once a month.
In a patent specification entitled xe2x80x9cMap Use Systemxe2x80x9d (Japanese Published Unexamined Patent Application No. Hei 8-44846), a method is disclosed which manages deleted and added geographic data in a geographic database and manages the geographic database when geographic data is modified at a time.
However, two problems have been identified with these methods: (1) search in time direction, for example, xe2x80x9cchange in the region in the last decadexe2x80x9d, requires reference to all past backup data; and (2) because all geographic data must be backed up, an enormous amount of time for backup and a large space to store history data will be required.
With the widespread use of Internet and Intranet, GISs have been adapted to network environments. With geographic information stored in a DB server, each user has become able to gain access to the server at the use""s terminal to obtain maps and other geographic information via a network. However, since geographic information generally has high volumes of data, there has been the problem of (3) increased communication time and increased load on networks.
Objects of the present invention are to solve the following problems:
(1) fast and easy search in time direction
(2) minimizing maintenance (backup) time and space to history data
(3) obtaining maps and other geographic information via a network with a minimum of communication time and load on the network
To achieve the above described objects, the present invention provides a feature data management method which handles as feature data each of a plurality of geographic objects such as houses and roads, and registers the feature data in a database for management. The feature data of the geographic objects includes creation time and destruction time data thereof, and when a geographic object is created, created time is stored in feature data thereof to register the feature data in the database, while when a geographic object is destroyed, destroyed time is stored in feature data thereof stored in the database to register the feature data in the database. Thereby, when time is specified to search for feature data of geographic objects registered in the database, the feature data of a geographic object that the specified time is between the created time and destroyed time can be obtained.
The present invention also offers a feature data management method which handles as each feature data of a plurality of geographic objects such as houses and roads, and registers the feature data in a database for management. As feature data of the geographic objects, data comprising a set of three items, feature changed time, name of the changed attribute, and differential value of the changed attribute, is provided. When a geographic object changes as time elapses, each time the change occurs, the feature data of the geographic object is registered to reflect the change in the database, in order that, of the set of data items as the feature data of the geographic object, change occurrence time is stored in the feature changed time item, a changed attribute of the feature is stored in the item of name of the changed attribute, and a change amount of the attribute is stored in the item of differential value of the changed attribute. Thereby, when time is specified to search for feature data of geographic objects registered in the database, the feature data of geographic objects containing changes which have occurred until the specified time can be obtained.
Feature datum of the geographic object has an unique ID number, and also has 2 ID numbers as its attributes, which point feature and past feature data respectively. When a geographic object changes as time elapses, feature data of the geographic object after the change is newly created, and in the new feature, the ID number of old feature is stored as the past feature, and in the old feature, the ID number of the new feature is stored as the future geographic object after the change is stored as ID number data of the future feature. Thereby, changes of geographic objects due to an elapse of time can be managed.
The present invention also offers a feature data management method which handles as feature data each of a plurality of geographic objects such as houses and roads, and with a collection of features treated as an area, registers feature data in a database for management, as one belonging to an area.
A huge feature extending beyond one area, like a road which crosses beyond many areas, is represented by a collection of features in each area. Each feature datum has an unique ID number, and also has 2 ID number as its attributes, which point of the feature data connected to the first point of the feature, and feature data connected the last point of the feature, respectively. Thereby huge geographic objects extending beyond one area can be managed.
Furthermore, when feature data is transferred to a client system connected to the database through a network, if the client system already obtains old feature data in the database, change differences between the old feature data in the database and feature data at a specified time are transferred to the client system.
In a case where the database is not searched on the basis of time and fast space search is required, only feature data existing at time of specification is extracted from the database, and a database from which time data is temporarily excluded is rebuilt by excluding the time data from the extracted feature data. Thereby fast space search is performed for the rebuilt database.
By setting feature rotation angle, parallel movement amount, and enlargement ratio as the change attributes, changes of geographic objects can be represented by a small number of parameters.